Starch supplement reduces the risk of some hereditary cancers

Taking a supplement of 30 grams of ‘resistant starch’ a day — about the amount in two slightly unripe bananas — reduced the risk of multiple forms of cancer in people with a rare genetic condition

By Grace Wade

Consuming resistant starch — a dietary fibre found in oatmeal, beans and bananas — reduces the risk of upper gastrointestinal cancers by nearly 50 per cent in people with Lynch syndrome. This is the first time a nutrient has been shown to prevent these cancers in people with the condition.

Lynch syndrome is a rare genetic disorder that increases the risk of many cancers including those found in the colon, brain, stomach and pancreas. The nutrient supplement finding is significant as upper gastrointestinal cancers tend to be the deadliest for people with Lynch syndrome, says Matthew Yurgelun at the Dana-Farber Cancer Institute in Boston, Massachusetts who was not involved in the work.

Research into resistant starch began almost half a century ago after some evidence suggested a high-fibre diet might lower the risk of colon cancer. This inspired John Mathers at Newcastle University in the UK to look at the role of resistant starch more closely, and some of his early research in colon cancer cells revealed that the nutrient had cancer-fighting properties.

To investigate further, Mathers and his colleagues had 463 people with Lynch syndrome supplement their diets with 30 grams of resistant starch per day for just over two years. This daily amount is roughly equivalent to what you would get from eating two slightly green bananas. Another 455 people received a placebo made of cornstarch.

“Cancer takes a long time to develop, but it develops more rapidly in people with Lynch syndrome. So, we though that working with people with Lynch syndrome could give us answers more quickly, and with a smaller number of people,” says Mathers.

Researchers collected data on cancer rates in all participants directly after the intervention and again after 10 years. They were also able to collect data after 20 years on 369 participants from England, Finland and Wales using national cancer registry databases.

After the initial two years, there was no difference in cancer rates among the two groups. However, combined data from each participant’s final follow-up showed that 78 people in the resistant starch group developed cancer compared to 96 in the control group, a statistically significant reduction in the incidence of cancer.

Though there was no difference in colon cancer rates between the two groups, there was a significant reduction in rates of upper gastrointestinal cancers such as pancreatic and stomach cancers. Only 5 people in the resistant starch group developed one of these conditions compared to 17 in the placebo group. “That’s where we saw a big reduction, roughly a 50 per cent reduction in cancer risk of those other non-colorectal cancers,” says Mathers.

“Resistant starch, like other forms of dietary fibre is a kind of food for the bacteria in our gut,” he says. “What we think is happening is that the extra resistant starch encourages the growth of certain bacteria and that then changed the metabolism of the bacteria.”

Bacteria in our gut can produce acids, called secondary bile acids, that are known to damage DNA. Mathers believes the resistant starch reduces how much of these acids gut bacteria produce, which in turn reduces DNA damage, and the less DNA damage someone has, the lower the risk of cancer.

“There are currently no evidence-based approaches to screening for or otherwise preventing [upper gastrointestinal] cancers in [people with] Lynch syndrome, so findings such as this are potentially quite impactful,” says Yurgelun.

Some previous research on cancer prevention methods in people with Lynch syndrome have ended up applying to the general population, so Mathers is hopeful the same is true for resistant starch. “But of course, we need to have further follow up studies in the general population,” he says.

Journal reference: Cancer Prevention Research, DOI: 10.1158/1940-6207.CAPR-22-0044

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